Discus b spins from thermal; aft CG and incomplete type check-out

While thermalling after an aerotow launch at Buttwil, a Discus b departed into an unrecovered spin; the pilot was fatally injured and the glider destroyed. After release at ~1 300 m MSL it had joined a thermal beneath another glider; the spin began from ~1 100 m MSL and no recovery attempt was observed before it struck a hangar roof, flipped and came to rest inverted on a second roof. The pilot had ~157 h total, only 1:18 h on type over three flights, and no record of spin training. The CG sat near the aft limit (cockpit minimum load 85 kg, pilot 75 kg equipped), and club familiarisation continued unsupervised after the first flight.

1. Aerotow from Buttwil: The pilot took an aerotow from RWY 34 at Buttwil for a local soaring flight in a single-seat Discus b, having flown three previous flights on the type totalling 1:18 h.
2. Aft CG and low time on type: The pilot weighed 75 kg against the airframe's required 85 kg minimum load; with 4.4 kg nose ballast the CG lay near the aft limit, where full rudder in a stall can provoke a spin.
3. Familiarisation flown unsupervised: The familiarisation programme called for three supervised flights; the pilot had one, then flew unsupervised thereafter, including this fourth flight on type.
4. Thermalling below another glider: The pilot released after ~4 minutes on tow at ~1,300 m MSL, roughly 700 m AGL, and joined a thermal beneath another glider at ~1,600 m MSL, later observed circling at ~1,100-1,150 m MSL.
5. Unintended spin from ~1 100 m MSL: The higher pilot saw the Discus b spin from ~1,100 m MSL (~500 m AGL), likely from dropping below the 68 km/h stall speed combined with the aft CG; recovery normally loses only 50-80 m.
6. No recovery attempt observed: Witnesses observed several spin rotations with no visible recovery attempt; the airspeed indicator showed just above 130 km/h at impact, consistent with continued spin to ground contact.
7. Roof impact; pilot fatally injured: The glider's nose struck a building's roof, the airframe somersaulted and came to rest inverted on a second roof; the pilot was ejected on impact and fatally injured, the aircraft destroyed.